Several different types of membraneless particle separation devices having a generally spiral or curved configuration have been described in U.S. patent application Ser. No. 11/606,460, filed Nov. 30, 2006, entitled “Particle Separation and Concentration System,” U.S. patent application Ser. No. 11/936,729, filed Nov. 7, 2007, entitled “Fluidic Device and Method for Separation of Neutrally Buoyant Particles,” U.S. application Ser. No. 11/936,753, filed Nov. 7, 2007, entitled “Device and Method for Dynamic Processing in Water Purification,” and co-pending, commonly assigned U.S. patent application Ser. No. 12/120,093, filed May 13, 2008, entitled “Fluidic Structures for Membraneless Particle Separation,” and naming Lean et al. as inventors.
In general, such devices are useful in connection with particles having density differences compared with water, thus creating centrifugal or buoyancy forces necessary for transverse migration through the channel for purposes of separation. Some of these devices are also useful, depending on their configuration to separate neutrally buoyant particles. With reference to FIG. 1, one example form of a separation device 20 is shown. This form shows an exemplary spiral channel 22 with increasing radius of curvature. This geometry takes advantage of the rate of pressure change. Any suitable form will suffice. However, for example, in another form, the device may have a contracting spiral channel with a decreasing radius of curvature for the sidewalls. The channel may also maintain a substantially constant radius of curvature and a constant channel size. In any of these cases, or others, the channel 22 evolves into two separate channels 24 and 26 (e.g. also referred to as channel #1 and channel #2 in FIG. 1 to allow for multiple outlet paths).
These types of separation devices provide for particle separation in a variety of manners. For example, depending on the flow rate, the particle separation may be driven by the centrifugal force or the pressure that is created by flow fluid through the channel. In any of these cases, the objective is for particle separation to occur. Typically the fluid flow will then have a first portion with particles of one type of particle or band and a second portion having fluid without the particles of the first portion therein.
In these types of systems, it would be desirable to provide for enhanced separation at the outlet of the devices.